Chapters 4 - Spokane Public Schools

CHAPTER 5: ECOSYSTEMS
Energy flow and nutrient cycles
The flow of
energy
Nutrients are
cycled through
the ecosystem
The importance
of decomposers
Energy flows from producers to consumers and eventually to
decomposers in an ecosystem. For example, when a mouse eats
seeds, energy stored in the seeds flows to the mouse. When a
hawk eats the mouse, energy flows from the mouse to the
hawk. The energy left in wastes and dead organisms flows to
the decomposers. At each step, some of that energy is lost in
the form of unusable heat. This means that energy is
continuously lost to the ecosystem. You will read more about
energy and ecosystems in the next section.
The energy available to the ecosystem is continuously lost
as unusable heat as it moves from one member to
another. Nutrients are different. Nutrients are the
elements and compounds needed by organisms to
stay alive. Nutrients like water, carbon, oxygen,
nitrogen, and calcium, are cycled through the
ecosystem and continuously reused. That’s why,
when scientists talk about the water or carbon in a
ecosystem, they use terms like “water cycle” or
“carbon-oxygen cycle.”
Decomposers play important roles in nutrient
cycles. Decomposers like fungi and bacteria
return nutrients to the soil, water, or air,
where they can again be used by the other living
members of the ecosystem. The diagram (right)
shows how living things are linked together by
energy and nutrients in ecosystems.
5.1 ECOSYSTEMS, ENERGY, AND NUTRIENTS
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